Annotation of src/usr.bin/ssh/sshd_config.5, Revision 1.150
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
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19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
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25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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1.150 ! djm 36: .\" $OpenBSD: sshd_config.5,v 1.149 2012/11/04 11:09:15 djm Exp $
1.149 djm 37: .Dd $Mdocdate: November 4 2012 $
1.1 stevesk 38: .Dt SSHD_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm sshd_config
42: .Nd OpenSSH SSH daemon configuration file
43: .Sh SYNOPSIS
1.71 jmc 44: .Nm /etc/ssh/sshd_config
1.1 stevesk 45: .Sh DESCRIPTION
1.53 jmc 46: .Xr sshd 8
1.1 stevesk 47: reads configuration data from
48: .Pa /etc/ssh/sshd_config
49: (or the file specified with
50: .Fl f
51: on the command line).
52: The file contains keyword-argument pairs, one per line.
53: Lines starting with
54: .Ql #
55: and empty lines are interpreted as comments.
1.56 dtucker 56: Arguments may optionally be enclosed in double quotes
57: .Pq \&"
58: in order to represent arguments containing spaces.
1.1 stevesk 59: .Pp
60: The possible
61: keywords and their meanings are as follows (note that
62: keywords are case-insensitive and arguments are case-sensitive):
63: .Bl -tag -width Ds
1.30 djm 64: .It Cm AcceptEnv
65: Specifies what environment variables sent by the client will be copied into
66: the session's
67: .Xr environ 7 .
68: See
69: .Cm SendEnv
70: in
71: .Xr ssh_config 5
72: for how to configure the client.
1.31 djm 73: Note that environment passing is only supported for protocol 2.
1.30 djm 74: Variables are specified by name, which may contain the wildcard characters
1.51 jmc 75: .Ql *
1.30 djm 76: and
77: .Ql \&? .
1.31 djm 78: Multiple environment variables may be separated by whitespace or spread
1.30 djm 79: across multiple
80: .Cm AcceptEnv
81: directives.
1.31 djm 82: Be warned that some environment variables could be used to bypass restricted
1.30 djm 83: user environments.
84: For this reason, care should be taken in the use of this directive.
85: The default is not to accept any environment variables.
1.37 djm 86: .It Cm AddressFamily
87: Specifies which address family should be used by
1.53 jmc 88: .Xr sshd 8 .
1.37 djm 89: Valid arguments are
90: .Dq any ,
91: .Dq inet
1.52 jmc 92: (use IPv4 only), or
1.37 djm 93: .Dq inet6
94: (use IPv6 only).
95: The default is
96: .Dq any .
1.89 jmc 97: .It Cm AllowAgentForwarding
98: Specifies whether
99: .Xr ssh-agent 1
100: forwarding is permitted.
101: The default is
102: .Dq yes .
103: Note that disabling agent forwarding does not improve security
104: unless users are also denied shell access, as they can always install
105: their own forwarders.
1.1 stevesk 106: .It Cm AllowGroups
107: This keyword can be followed by a list of group name patterns, separated
108: by spaces.
109: If specified, login is allowed only for users whose primary
110: group or supplementary group list matches one of the patterns.
111: Only group names are valid; a numerical group ID is not recognized.
112: By default, login is allowed for all groups.
1.54 jmc 113: The allow/deny directives are processed in the following order:
114: .Cm DenyUsers ,
115: .Cm AllowUsers ,
116: .Cm DenyGroups ,
117: and finally
118: .Cm AllowGroups .
1.49 jmc 119: .Pp
120: See
121: .Sx PATTERNS
122: in
123: .Xr ssh_config 5
124: for more information on patterns.
1.1 stevesk 125: .It Cm AllowTcpForwarding
126: Specifies whether TCP forwarding is permitted.
1.150 ! djm 127: The available options are
! 128: .Dq yes
! 129: or
! 130: .Dq all
! 131: to allow TCP forwarding,
! 132: .Dq no
! 133: to prevent all TCP forwarding,
! 134: .Dq local
! 135: to allow local (from the perspective of
! 136: .Xr ssh 1 ) forwarding only or
! 137: .Dq remote
! 138: to allow remote forwarding only.
1.1 stevesk 139: The default is
140: .Dq yes .
141: Note that disabling TCP forwarding does not improve security unless
142: users are also denied shell access, as they can always install their
143: own forwarders.
144: .It Cm AllowUsers
145: This keyword can be followed by a list of user name patterns, separated
146: by spaces.
1.14 jmc 147: If specified, login is allowed only for user names that
1.1 stevesk 148: match one of the patterns.
149: Only user names are valid; a numerical user ID is not recognized.
150: By default, login is allowed for all users.
151: If the pattern takes the form USER@HOST then USER and HOST
152: are separately checked, restricting logins to particular
153: users from particular hosts.
1.54 jmc 154: The allow/deny directives are processed in the following order:
155: .Cm DenyUsers ,
156: .Cm AllowUsers ,
157: .Cm DenyGroups ,
158: and finally
159: .Cm AllowGroups .
1.49 jmc 160: .Pp
161: See
162: .Sx PATTERNS
163: in
164: .Xr ssh_config 5
165: for more information on patterns.
1.149 djm 166: .It Cm AuthenticationMethods
167: Specifies the authentication methods that must be successfully completed
168: for a user to be granted access.
169: This option must be followed by one or more comma-separated lists of
170: authentication method names.
171: Successful authentication requires completion of every method in at least
172: one of these lists.
173: .Pp
174: For example, an argument of
175: .Dq publickey,password publickey,keyboard-interactive
176: would require the user to complete public key authentication, followed by
177: either password or keyboard interactive authentication.
178: Only methods that are next in one or more lists are offered at each stage,
179: so for this example, it would not be possible to attempt password or
180: keyboard-interactive authentication before public key.
181: .Pp
182: This option is only available for SSH protocol 2 and will yield a fatal
183: error if enabled if protocol 1 is also enabled.
184: Note that each authentication method listed should also be explicitly enabled
185: in the configuration.
186: The default is not to require multiple authentication; successful completion
187: of a single authentication method is sufficient.
1.146 djm 188: .It Cm AuthorizedKeysCommand
1.147 jmc 189: Specifies a program to be used to look up the user's public keys.
1.146 djm 190: The program will be invoked with a single argument of the username
191: being authenticated, and should produce on standard output zero or
1.147 jmc 192: more lines of authorized_keys output (see
193: .Sx AUTHORIZED_KEYS
194: in
195: .Xr sshd 8 ) .
1.146 djm 196: If a key supplied by AuthorizedKeysCommand does not successfully authenticate
197: and authorize the user then public key authentication continues using the usual
198: .Cm AuthorizedKeysFile
199: files.
200: By default, no AuthorizedKeysCommand is run.
201: .It Cm AuthorizedKeysCommandUser
202: Specifies the user under whose account the AuthorizedKeysCommand is run.
203: It is recommended to use a dedicated user that has no other role on the host
204: than running authorized keys commands.
1.1 stevesk 205: .It Cm AuthorizedKeysFile
206: Specifies the file that contains the public keys that can be used
207: for user authentication.
1.124 djm 208: The format is described in the
209: .Sx AUTHORIZED_KEYS FILE FORMAT
210: section of
211: .Xr sshd 8 .
1.1 stevesk 212: .Cm AuthorizedKeysFile
213: may contain tokens of the form %T which are substituted during connection
1.52 jmc 214: setup.
1.17 jmc 215: The following tokens are defined: %% is replaced by a literal '%',
1.52 jmc 216: %h is replaced by the home directory of the user being authenticated, and
1.1 stevesk 217: %u is replaced by the username of that user.
218: After expansion,
219: .Cm AuthorizedKeysFile
220: is taken to be an absolute path or one relative to the user's home
221: directory.
1.133 jmc 222: Multiple files may be listed, separated by whitespace.
223: The default is
224: .Dq .ssh/authorized_keys .ssh/authorized_keys2 .
1.121 djm 225: .It Cm AuthorizedPrincipalsFile
226: Specifies a file that lists principal names that are accepted for
227: certificate authentication.
228: When using certificates signed by a key listed in
229: .Cm TrustedUserCAKeys ,
230: this file lists names, one of which must appear in the certificate for it
231: to be accepted for authentication.
1.125 jmc 232: Names are listed one per line preceded by key options (as described
1.124 djm 233: in
234: .Sx AUTHORIZED_KEYS FILE FORMAT
235: in
1.125 jmc 236: .Xr sshd 8 ) .
1.124 djm 237: Empty lines and comments starting with
1.121 djm 238: .Ql #
239: are ignored.
240: .Pp
241: .Cm AuthorizedPrincipalsFile
242: may contain tokens of the form %T which are substituted during connection
243: setup.
244: The following tokens are defined: %% is replaced by a literal '%',
245: %h is replaced by the home directory of the user being authenticated, and
246: %u is replaced by the username of that user.
247: After expansion,
248: .Cm AuthorizedPrincipalsFile
249: is taken to be an absolute path or one relative to the user's home
250: directory.
251: .Pp
1.138 djm 252: The default is
253: .Dq none ,
254: i.e. not to use a principals file \(en in this case, the username
1.121 djm 255: of the user must appear in a certificate's principals list for it to be
256: accepted.
257: Note that
258: .Cm AuthorizedPrincipalsFile
259: is only used when authentication proceeds using a CA listed in
260: .Cm TrustedUserCAKeys
261: and is not consulted for certification authorities trusted via
262: .Pa ~/.ssh/authorized_keys ,
263: though the
264: .Cm principals=
265: key option offers a similar facility (see
266: .Xr sshd 8
267: for details).
1.1 stevesk 268: .It Cm Banner
269: The contents of the specified file are sent to the remote user before
270: authentication is allowed.
1.78 djm 271: If the argument is
272: .Dq none
273: then no banner is displayed.
1.1 stevesk 274: This option is only available for protocol version 2.
275: By default, no banner is displayed.
276: .It Cm ChallengeResponseAuthentication
1.50 jmc 277: Specifies whether challenge-response authentication is allowed.
1.1 stevesk 278: All authentication styles from
279: .Xr login.conf 5
280: are supported.
281: The default is
282: .Dq yes .
1.80 djm 283: .It Cm ChrootDirectory
1.113 stevesk 284: Specifies the pathname of a directory to
1.80 djm 285: .Xr chroot 2
286: to after authentication.
1.113 stevesk 287: All components of the pathname must be root-owned directories that are
1.80 djm 288: not writable by any other user or group.
1.106 stevesk 289: After the chroot,
290: .Xr sshd 8
291: changes the working directory to the user's home directory.
1.80 djm 292: .Pp
1.113 stevesk 293: The pathname may contain the following tokens that are expanded at runtime once
1.80 djm 294: the connecting user has been authenticated: %% is replaced by a literal '%',
295: %h is replaced by the home directory of the user being authenticated, and
296: %u is replaced by the username of that user.
297: .Pp
298: The
299: .Cm ChrootDirectory
300: must contain the necessary files and directories to support the
1.103 stevesk 301: user's session.
1.80 djm 302: For an interactive session this requires at least a shell, typically
303: .Xr sh 1 ,
304: and basic
305: .Pa /dev
306: nodes such as
307: .Xr null 4 ,
308: .Xr zero 4 ,
309: .Xr stdin 4 ,
310: .Xr stdout 4 ,
311: .Xr stderr 4 ,
312: .Xr arandom 4
313: and
314: .Xr tty 4
315: devices.
316: For file transfer sessions using
1.105 jmc 317: .Dq sftp ,
1.80 djm 318: no additional configuration of the environment is necessary if the
1.105 jmc 319: in-process sftp server is used,
320: though sessions which use logging do require
1.104 stevesk 321: .Pa /dev/log
322: inside the chroot directory (see
323: .Xr sftp-server 8
1.81 jmc 324: for details).
1.80 djm 325: .Pp
326: The default is not to
327: .Xr chroot 2 .
1.1 stevesk 328: .It Cm Ciphers
329: Specifies the ciphers allowed for protocol version 2.
330: Multiple ciphers must be comma-separated.
1.34 dtucker 331: The supported ciphers are
332: .Dq 3des-cbc ,
333: .Dq aes128-cbc ,
334: .Dq aes192-cbc ,
335: .Dq aes256-cbc ,
336: .Dq aes128-ctr ,
337: .Dq aes192-ctr ,
338: .Dq aes256-ctr ,
1.43 djm 339: .Dq arcfour128 ,
340: .Dq arcfour256 ,
1.34 dtucker 341: .Dq arcfour ,
342: .Dq blowfish-cbc ,
343: and
344: .Dq cast128-cbc .
1.52 jmc 345: The default is:
346: .Bd -literal -offset 3n
1.100 naddy 347: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
348: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
349: aes256-cbc,arcfour
1.1 stevesk 350: .Ed
351: .It Cm ClientAliveCountMax
1.48 jmc 352: Sets the number of client alive messages (see below) which may be
1.1 stevesk 353: sent without
1.52 jmc 354: .Xr sshd 8
1.17 jmc 355: receiving any messages back from the client.
356: If this threshold is reached while client alive messages are being sent,
1.52 jmc 357: sshd will disconnect the client, terminating the session.
1.17 jmc 358: It is important to note that the use of client alive messages is very
359: different from
1.27 markus 360: .Cm TCPKeepAlive
1.17 jmc 361: (below).
362: The client alive messages are sent through the encrypted channel
363: and therefore will not be spoofable.
364: The TCP keepalive option enabled by
1.27 markus 365: .Cm TCPKeepAlive
1.17 jmc 366: is spoofable.
367: The client alive mechanism is valuable when the client or
1.1 stevesk 368: server depend on knowing when a connection has become inactive.
369: .Pp
1.17 jmc 370: The default value is 3.
371: If
1.1 stevesk 372: .Cm ClientAliveInterval
1.48 jmc 373: (see below) is set to 15, and
1.1 stevesk 374: .Cm ClientAliveCountMax
1.52 jmc 375: is left at the default, unresponsive SSH clients
1.1 stevesk 376: will be disconnected after approximately 45 seconds.
1.57 markus 377: This option applies to protocol version 2 only.
1.42 djm 378: .It Cm ClientAliveInterval
379: Sets a timeout interval in seconds after which if no data has been received
380: from the client,
1.52 jmc 381: .Xr sshd 8
1.42 djm 382: will send a message through the encrypted
383: channel to request a response from the client.
384: The default
385: is 0, indicating that these messages will not be sent to the client.
386: This option applies to protocol version 2 only.
1.3 markus 387: .It Cm Compression
1.44 markus 388: Specifies whether compression is allowed, or delayed until
389: the user has authenticated successfully.
1.3 markus 390: The argument must be
1.44 markus 391: .Dq yes ,
392: .Dq delayed ,
1.3 markus 393: or
394: .Dq no .
395: The default is
1.44 markus 396: .Dq delayed .
1.1 stevesk 397: .It Cm DenyGroups
398: This keyword can be followed by a list of group name patterns, separated
399: by spaces.
400: Login is disallowed for users whose primary group or supplementary
401: group list matches one of the patterns.
402: Only group names are valid; a numerical group ID is not recognized.
403: By default, login is allowed for all groups.
1.54 jmc 404: The allow/deny directives are processed in the following order:
405: .Cm DenyUsers ,
406: .Cm AllowUsers ,
407: .Cm DenyGroups ,
408: and finally
409: .Cm AllowGroups .
1.49 jmc 410: .Pp
411: See
412: .Sx PATTERNS
413: in
414: .Xr ssh_config 5
415: for more information on patterns.
1.1 stevesk 416: .It Cm DenyUsers
417: This keyword can be followed by a list of user name patterns, separated
418: by spaces.
419: Login is disallowed for user names that match one of the patterns.
420: Only user names are valid; a numerical user ID is not recognized.
421: By default, login is allowed for all users.
422: If the pattern takes the form USER@HOST then USER and HOST
423: are separately checked, restricting logins to particular
424: users from particular hosts.
1.54 jmc 425: The allow/deny directives are processed in the following order:
426: .Cm DenyUsers ,
427: .Cm AllowUsers ,
428: .Cm DenyGroups ,
429: and finally
430: .Cm AllowGroups .
1.49 jmc 431: .Pp
432: See
433: .Sx PATTERNS
434: in
435: .Xr ssh_config 5
436: for more information on patterns.
1.67 dtucker 437: .It Cm ForceCommand
438: Forces the execution of the command specified by
439: .Cm ForceCommand ,
1.84 djm 440: ignoring any command supplied by the client and
441: .Pa ~/.ssh/rc
442: if present.
1.67 dtucker 443: The command is invoked by using the user's login shell with the -c option.
444: This applies to shell, command, or subsystem execution.
445: It is most useful inside a
446: .Cm Match
447: block.
448: The command originally supplied by the client is available in the
449: .Ev SSH_ORIGINAL_COMMAND
450: environment variable.
1.82 djm 451: Specifying a command of
452: .Dq internal-sftp
453: will force the use of an in-process sftp server that requires no support
454: files when used with
455: .Cm ChrootDirectory .
1.1 stevesk 456: .It Cm GatewayPorts
457: Specifies whether remote hosts are allowed to connect to ports
458: forwarded for the client.
459: By default,
1.52 jmc 460: .Xr sshd 8
1.15 jmc 461: binds remote port forwardings to the loopback address.
462: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 463: .Cm GatewayPorts
1.52 jmc 464: can be used to specify that sshd
1.39 djm 465: should allow remote port forwardings to bind to non-loopback addresses, thus
466: allowing other hosts to connect.
467: The argument may be
468: .Dq no
469: to force remote port forwardings to be available to the local host only,
1.1 stevesk 470: .Dq yes
1.39 djm 471: to force remote port forwardings to bind to the wildcard address, or
472: .Dq clientspecified
473: to allow the client to select the address to which the forwarding is bound.
1.1 stevesk 474: The default is
475: .Dq no .
1.23 markus 476: .It Cm GSSAPIAuthentication
1.25 markus 477: Specifies whether user authentication based on GSSAPI is allowed.
1.26 djm 478: The default is
1.23 markus 479: .Dq no .
480: Note that this option applies to protocol version 2 only.
481: .It Cm GSSAPICleanupCredentials
482: Specifies whether to automatically destroy the user's credentials cache
483: on logout.
484: The default is
485: .Dq yes .
486: Note that this option applies to protocol version 2 only.
1.1 stevesk 487: .It Cm HostbasedAuthentication
488: Specifies whether rhosts or /etc/hosts.equiv authentication together
489: with successful public key client host authentication is allowed
1.50 jmc 490: (host-based authentication).
1.1 stevesk 491: This option is similar to
492: .Cm RhostsRSAAuthentication
493: and applies to protocol version 2 only.
1.70 dtucker 494: The default is
495: .Dq no .
496: .It Cm HostbasedUsesNameFromPacketOnly
497: Specifies whether or not the server will attempt to perform a reverse
498: name lookup when matching the name in the
499: .Pa ~/.shosts ,
500: .Pa ~/.rhosts ,
501: and
502: .Pa /etc/hosts.equiv
503: files during
504: .Cm HostbasedAuthentication .
505: A setting of
506: .Dq yes
507: means that
508: .Xr sshd 8
509: uses the name supplied by the client rather than
510: attempting to resolve the name from the TCP connection itself.
1.1 stevesk 511: The default is
512: .Dq no .
1.117 djm 513: .It Cm HostCertificate
514: Specifies a file containing a public host certificate.
515: The certificate's public key must match a private host key already specified
516: by
517: .Cm HostKey .
518: The default behaviour of
519: .Xr sshd 8
520: is not to load any certificates.
1.1 stevesk 521: .It Cm HostKey
522: Specifies a file containing a private host key
523: used by SSH.
524: The default is
525: .Pa /etc/ssh/ssh_host_key
526: for protocol version 1, and
1.126 djm 527: .Pa /etc/ssh/ssh_host_dsa_key ,
528: .Pa /etc/ssh/ssh_host_ecdsa_key
529: and
1.1 stevesk 530: .Pa /etc/ssh/ssh_host_rsa_key
531: for protocol version 2.
532: Note that
1.52 jmc 533: .Xr sshd 8
1.1 stevesk 534: will refuse to use a file if it is group/world-accessible.
535: It is possible to have multiple host key files.
536: .Dq rsa1
537: keys are used for version 1 and
1.126 djm 538: .Dq dsa ,
539: .Dq ecdsa
1.1 stevesk 540: or
541: .Dq rsa
542: are used for version 2 of the SSH protocol.
543: .It Cm IgnoreRhosts
544: Specifies that
545: .Pa .rhosts
546: and
547: .Pa .shosts
548: files will not be used in
549: .Cm RhostsRSAAuthentication
550: or
551: .Cm HostbasedAuthentication .
552: .Pp
553: .Pa /etc/hosts.equiv
554: and
555: .Pa /etc/shosts.equiv
556: are still used.
557: The default is
558: .Dq yes .
559: .It Cm IgnoreUserKnownHosts
560: Specifies whether
1.52 jmc 561: .Xr sshd 8
1.1 stevesk 562: should ignore the user's
1.41 djm 563: .Pa ~/.ssh/known_hosts
1.1 stevesk 564: during
565: .Cm RhostsRSAAuthentication
566: or
567: .Cm HostbasedAuthentication .
568: The default is
569: .Dq no .
1.129 djm 570: .It Cm IPQoS
571: Specifies the IPv4 type-of-service or DSCP class for the connection.
572: Accepted values are
573: .Dq af11 ,
574: .Dq af12 ,
575: .Dq af13 ,
1.136 djm 576: .Dq af21 ,
1.129 djm 577: .Dq af22 ,
578: .Dq af23 ,
579: .Dq af31 ,
580: .Dq af32 ,
581: .Dq af33 ,
582: .Dq af41 ,
583: .Dq af42 ,
584: .Dq af43 ,
585: .Dq cs0 ,
586: .Dq cs1 ,
587: .Dq cs2 ,
588: .Dq cs3 ,
589: .Dq cs4 ,
590: .Dq cs5 ,
591: .Dq cs6 ,
592: .Dq cs7 ,
593: .Dq ef ,
594: .Dq lowdelay ,
595: .Dq throughput ,
596: .Dq reliability ,
597: or a numeric value.
1.131 djm 598: This option may take one or two arguments, separated by whitespace.
1.129 djm 599: If one argument is specified, it is used as the packet class unconditionally.
600: If two values are specified, the first is automatically selected for
601: interactive sessions and the second for non-interactive sessions.
602: The default is
603: .Dq lowdelay
604: for interactive sessions and
605: .Dq throughput
606: for non-interactive sessions.
1.1 stevesk 607: .It Cm KerberosAuthentication
1.24 markus 608: Specifies whether the password provided by the user for
1.1 stevesk 609: .Cm PasswordAuthentication
1.24 markus 610: will be validated through the Kerberos KDC.
1.1 stevesk 611: To use this option, the server needs a
612: Kerberos servtab which allows the verification of the KDC's identity.
1.52 jmc 613: The default is
1.29 dtucker 614: .Dq no .
615: .It Cm KerberosGetAFSToken
1.45 djm 616: If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire
1.29 dtucker 617: an AFS token before accessing the user's home directory.
1.52 jmc 618: The default is
1.1 stevesk 619: .Dq no .
620: .It Cm KerberosOrLocalPasswd
1.52 jmc 621: If password authentication through Kerberos fails then
1.1 stevesk 622: the password will be validated via any additional local mechanism
623: such as
624: .Pa /etc/passwd .
1.52 jmc 625: The default is
1.1 stevesk 626: .Dq yes .
627: .It Cm KerberosTicketCleanup
628: Specifies whether to automatically destroy the user's ticket cache
629: file on logout.
1.52 jmc 630: The default is
1.1 stevesk 631: .Dq yes .
1.127 djm 632: .It Cm KexAlgorithms
633: Specifies the available KEX (Key Exchange) algorithms.
634: Multiple algorithms must be comma-separated.
635: The default is
636: .Dq ecdh-sha2-nistp256 ,
637: .Dq ecdh-sha2-nistp384 ,
638: .Dq ecdh-sha2-nistp521 ,
1.130 jmc 639: .Dq diffie-hellman-group-exchange-sha256 ,
1.127 djm 640: .Dq diffie-hellman-group-exchange-sha1 ,
641: .Dq diffie-hellman-group14-sha1 ,
642: .Dq diffie-hellman-group1-sha1 .
1.1 stevesk 643: .It Cm KeyRegenerationInterval
644: In protocol version 1, the ephemeral server key is automatically regenerated
645: after this many seconds (if it has been used).
646: The purpose of regeneration is to prevent
647: decrypting captured sessions by later breaking into the machine and
648: stealing the keys.
649: The key is never stored anywhere.
650: If the value is 0, the key is never regenerated.
651: The default is 3600 (seconds).
652: .It Cm ListenAddress
653: Specifies the local addresses
1.52 jmc 654: .Xr sshd 8
1.1 stevesk 655: should listen on.
656: The following forms may be used:
657: .Pp
658: .Bl -item -offset indent -compact
659: .It
660: .Cm ListenAddress
661: .Sm off
662: .Ar host No | Ar IPv4_addr No | Ar IPv6_addr
663: .Sm on
664: .It
665: .Cm ListenAddress
666: .Sm off
667: .Ar host No | Ar IPv4_addr No : Ar port
668: .Sm on
669: .It
670: .Cm ListenAddress
671: .Sm off
672: .Oo
673: .Ar host No | Ar IPv6_addr Oc : Ar port
674: .Sm on
675: .El
676: .Pp
677: If
678: .Ar port
679: is not specified,
1.52 jmc 680: sshd will listen on the address and all prior
1.1 stevesk 681: .Cm Port
1.17 jmc 682: options specified.
683: The default is to listen on all local addresses.
1.15 jmc 684: Multiple
1.1 stevesk 685: .Cm ListenAddress
1.17 jmc 686: options are permitted.
687: Additionally, any
1.1 stevesk 688: .Cm Port
1.52 jmc 689: options must precede this option for non-port qualified addresses.
1.1 stevesk 690: .It Cm LoginGraceTime
691: The server disconnects after this time if the user has not
692: successfully logged in.
693: If the value is 0, there is no time limit.
1.12 stevesk 694: The default is 120 seconds.
1.1 stevesk 695: .It Cm LogLevel
696: Gives the verbosity level that is used when logging messages from
1.53 jmc 697: .Xr sshd 8 .
1.1 stevesk 698: The possible values are:
1.52 jmc 699: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.15 jmc 700: The default is INFO.
701: DEBUG and DEBUG1 are equivalent.
702: DEBUG2 and DEBUG3 each specify higher levels of debugging output.
703: Logging with a DEBUG level violates the privacy of users and is not recommended.
1.1 stevesk 704: .It Cm MACs
705: Specifies the available MAC (message authentication code) algorithms.
706: The MAC algorithm is used in protocol version 2
707: for data integrity protection.
708: Multiple algorithms must be comma-separated.
1.52 jmc 709: The default is:
1.77 jmc 710: .Bd -literal -offset indent
1.145 markus 711: hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
1.144 naddy 712: hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
713: hmac-sha1-96,hmac-md5-96
1.77 jmc 714: .Ed
1.60 dtucker 715: .It Cm Match
1.61 jmc 716: Introduces a conditional block.
1.65 dtucker 717: If all of the criteria on the
1.60 dtucker 718: .Cm Match
1.65 dtucker 719: line are satisfied, the keywords on the following lines override those
720: set in the global section of the config file, until either another
1.60 dtucker 721: .Cm Match
1.65 dtucker 722: line or the end of the file.
1.91 djm 723: .Pp
1.61 jmc 724: The arguments to
1.60 dtucker 725: .Cm Match
1.65 dtucker 726: are one or more criteria-pattern pairs.
1.60 dtucker 727: The available criteria are
728: .Cm User ,
1.69 dtucker 729: .Cm Group ,
1.60 dtucker 730: .Cm Host ,
1.139 dtucker 731: .Cm LocalAddress ,
732: .Cm LocalPort ,
1.60 dtucker 733: and
734: .Cm Address .
1.91 djm 735: The match patterns may consist of single entries or comma-separated
736: lists and may use the wildcard and negation operators described in the
1.92 djm 737: .Sx PATTERNS
1.91 djm 738: section of
1.92 djm 739: .Xr ssh_config 5 .
1.91 djm 740: .Pp
741: The patterns in an
742: .Cm Address
743: criteria may additionally contain addresses to match in CIDR
1.93 jmc 744: address/masklen format, e.g.\&
1.91 djm 745: .Dq 192.0.2.0/24
746: or
747: .Dq 3ffe:ffff::/32 .
748: Note that the mask length provided must be consistent with the address -
749: it is an error to specify a mask length that is too long for the address
1.93 jmc 750: or one with bits set in this host portion of the address.
751: For example,
1.91 djm 752: .Dq 192.0.2.0/33
753: and
1.93 jmc 754: .Dq 192.0.2.0/8
1.91 djm 755: respectively.
756: .Pp
1.60 dtucker 757: Only a subset of keywords may be used on the lines following a
758: .Cm Match
759: keyword.
760: Available keywords are
1.142 jmc 761: .Cm AcceptEnv ,
1.99 okan 762: .Cm AllowAgentForwarding ,
1.142 jmc 763: .Cm AllowGroups ,
1.62 dtucker 764: .Cm AllowTcpForwarding ,
1.141 markus 765: .Cm AllowUsers ,
1.149 djm 766: .Cm AuthenticationMethods ,
1.146 djm 767: .Cm AuthorizedKeysCommand ,
768: .Cm AuthorizedKeysCommandUser ,
1.147 jmc 769: .Cm AuthorizedKeysFile ,
1.123 djm 770: .Cm AuthorizedPrincipalsFile ,
1.72 dtucker 771: .Cm Banner ,
1.85 djm 772: .Cm ChrootDirectory ,
1.141 markus 773: .Cm DenyGroups ,
774: .Cm DenyUsers ,
1.67 dtucker 775: .Cm ForceCommand ,
1.142 jmc 776: .Cm GatewayPorts ,
1.141 markus 777: .Cm GSSAPIAuthentication ,
1.87 djm 778: .Cm HostbasedAuthentication ,
1.123 djm 779: .Cm HostbasedUsesNameFromPacketOnly ,
1.74 jmc 780: .Cm KbdInteractiveAuthentication ,
1.72 dtucker 781: .Cm KerberosAuthentication ,
1.95 dtucker 782: .Cm MaxAuthTries ,
1.94 dtucker 783: .Cm MaxSessions ,
1.72 dtucker 784: .Cm PasswordAuthentication ,
1.97 djm 785: .Cm PermitEmptyPasswords ,
1.66 dtucker 786: .Cm PermitOpen ,
1.79 dtucker 787: .Cm PermitRootLogin ,
1.123 djm 788: .Cm PermitTunnel ,
1.107 dtucker 789: .Cm PubkeyAuthentication ,
1.142 jmc 790: .Cm RhostsRSAAuthentication ,
1.141 markus 791: .Cm RSAAuthentication ,
1.66 dtucker 792: .Cm X11DisplayOffset ,
1.101 djm 793: .Cm X11Forwarding
1.60 dtucker 794: and
1.102 djm 795: .Cm X11UseLocalHost .
1.33 dtucker 796: .It Cm MaxAuthTries
797: Specifies the maximum number of authentication attempts permitted per
1.35 jmc 798: connection.
799: Once the number of failures reaches half this value,
800: additional failures are logged.
801: The default is 6.
1.90 djm 802: .It Cm MaxSessions
803: Specifies the maximum number of open sessions permitted per network connection.
804: The default is 10.
1.1 stevesk 805: .It Cm MaxStartups
806: Specifies the maximum number of concurrent unauthenticated connections to the
1.52 jmc 807: SSH daemon.
1.1 stevesk 808: Additional connections will be dropped until authentication succeeds or the
809: .Cm LoginGraceTime
810: expires for a connection.
811: The default is 10.
812: .Pp
813: Alternatively, random early drop can be enabled by specifying
814: the three colon separated values
815: .Dq start:rate:full
1.51 jmc 816: (e.g. "10:30:60").
1.53 jmc 817: .Xr sshd 8
1.1 stevesk 818: will refuse connection attempts with a probability of
819: .Dq rate/100
820: (30%)
821: if there are currently
822: .Dq start
823: (10)
824: unauthenticated connections.
825: The probability increases linearly and all connection attempts
826: are refused if the number of unauthenticated connections reaches
827: .Dq full
828: (60).
829: .It Cm PasswordAuthentication
830: Specifies whether password authentication is allowed.
831: The default is
832: .Dq yes .
833: .It Cm PermitEmptyPasswords
834: When password authentication is allowed, it specifies whether the
835: server allows login to accounts with empty password strings.
836: The default is
837: .Dq no .
1.62 dtucker 838: .It Cm PermitOpen
839: Specifies the destinations to which TCP port forwarding is permitted.
840: The forwarding specification must be one of the following forms:
841: .Pp
842: .Bl -item -offset indent -compact
843: .It
844: .Cm PermitOpen
845: .Sm off
846: .Ar host : port
847: .Sm on
848: .It
849: .Cm PermitOpen
850: .Sm off
851: .Ar IPv4_addr : port
852: .Sm on
853: .It
854: .Cm PermitOpen
855: .Sm off
856: .Ar \&[ IPv6_addr \&] : port
857: .Sm on
858: .El
859: .Pp
1.68 dtucker 860: Multiple forwards may be specified by separating them with whitespace.
1.62 dtucker 861: An argument of
862: .Dq any
863: can be used to remove all restrictions and permit any forwarding requests.
1.140 dtucker 864: An argument of
865: .Dq none
866: can be used to prohibit all forwarding requests.
1.63 jmc 867: By default all port forwarding requests are permitted.
1.1 stevesk 868: .It Cm PermitRootLogin
1.38 jmc 869: Specifies whether root can log in using
1.1 stevesk 870: .Xr ssh 1 .
871: The argument must be
872: .Dq yes ,
873: .Dq without-password ,
1.52 jmc 874: .Dq forced-commands-only ,
1.1 stevesk 875: or
876: .Dq no .
877: The default is
878: .Dq yes .
879: .Pp
880: If this option is set to
1.52 jmc 881: .Dq without-password ,
1.1 stevesk 882: password authentication is disabled for root.
883: .Pp
884: If this option is set to
1.52 jmc 885: .Dq forced-commands-only ,
1.1 stevesk 886: root login with public key authentication will be allowed,
887: but only if the
888: .Ar command
889: option has been specified
890: (which may be useful for taking remote backups even if root login is
1.17 jmc 891: normally not allowed).
892: All other authentication methods are disabled for root.
1.1 stevesk 893: .Pp
894: If this option is set to
1.52 jmc 895: .Dq no ,
1.38 jmc 896: root is not allowed to log in.
1.46 reyk 897: .It Cm PermitTunnel
898: Specifies whether
899: .Xr tun 4
900: device forwarding is allowed.
1.47 reyk 901: The argument must be
902: .Dq yes ,
1.58 stevesk 903: .Dq point-to-point
904: (layer 3),
905: .Dq ethernet
906: (layer 2), or
1.47 reyk 907: .Dq no .
1.58 stevesk 908: Specifying
909: .Dq yes
910: permits both
911: .Dq point-to-point
912: and
913: .Dq ethernet .
1.46 reyk 914: The default is
915: .Dq no .
1.6 markus 916: .It Cm PermitUserEnvironment
917: Specifies whether
918: .Pa ~/.ssh/environment
1.9 stevesk 919: and
1.6 markus 920: .Cm environment=
921: options in
922: .Pa ~/.ssh/authorized_keys
1.9 stevesk 923: are processed by
1.52 jmc 924: .Xr sshd 8 .
1.6 markus 925: The default is
926: .Dq no .
1.9 stevesk 927: Enabling environment processing may enable users to bypass access
928: restrictions in some configurations using mechanisms such as
929: .Ev LD_PRELOAD .
1.1 stevesk 930: .It Cm PidFile
1.4 stevesk 931: Specifies the file that contains the process ID of the
1.53 jmc 932: SSH daemon.
1.1 stevesk 933: The default is
934: .Pa /var/run/sshd.pid .
935: .It Cm Port
936: Specifies the port number that
1.52 jmc 937: .Xr sshd 8
1.1 stevesk 938: listens on.
939: The default is 22.
940: Multiple options of this type are permitted.
941: See also
942: .Cm ListenAddress .
943: .It Cm PrintLastLog
944: Specifies whether
1.52 jmc 945: .Xr sshd 8
1.36 jaredy 946: should print the date and time of the last user login when a user logs
947: in interactively.
1.1 stevesk 948: The default is
949: .Dq yes .
950: .It Cm PrintMotd
951: Specifies whether
1.52 jmc 952: .Xr sshd 8
1.1 stevesk 953: should print
954: .Pa /etc/motd
955: when a user logs in interactively.
956: (On some systems it is also printed by the shell,
957: .Pa /etc/profile ,
958: or equivalent.)
959: The default is
960: .Dq yes .
961: .It Cm Protocol
962: Specifies the protocol versions
1.52 jmc 963: .Xr sshd 8
1.5 stevesk 964: supports.
1.1 stevesk 965: The possible values are
1.52 jmc 966: .Sq 1
1.1 stevesk 967: and
1.52 jmc 968: .Sq 2 .
1.1 stevesk 969: Multiple versions must be comma-separated.
970: The default is
1.109 jmc 971: .Sq 2 .
1.5 stevesk 972: Note that the order of the protocol list does not indicate preference,
973: because the client selects among multiple protocol versions offered
974: by the server.
975: Specifying
976: .Dq 2,1
977: is identical to
978: .Dq 1,2 .
1.1 stevesk 979: .It Cm PubkeyAuthentication
980: Specifies whether public key authentication is allowed.
981: The default is
982: .Dq yes .
983: Note that this option applies to protocol version 2 only.
1.118 djm 984: .It Cm RevokedKeys
985: Specifies a list of revoked public keys.
986: Keys listed in this file will be refused for public key authentication.
987: Note that if this file is not readable, then public key authentication will
988: be refused for all users.
1.1 stevesk 989: .It Cm RhostsRSAAuthentication
990: Specifies whether rhosts or /etc/hosts.equiv authentication together
991: with successful RSA host authentication is allowed.
992: The default is
993: .Dq no .
994: This option applies to protocol version 1 only.
995: .It Cm RSAAuthentication
996: Specifies whether pure RSA authentication is allowed.
997: The default is
998: .Dq yes .
999: This option applies to protocol version 1 only.
1000: .It Cm ServerKeyBits
1001: Defines the number of bits in the ephemeral protocol version 1 server key.
1.96 djm 1002: The minimum value is 512, and the default is 1024.
1.1 stevesk 1003: .It Cm StrictModes
1004: Specifies whether
1.52 jmc 1005: .Xr sshd 8
1.1 stevesk 1006: should check file modes and ownership of the
1007: user's files and home directory before accepting login.
1008: This is normally desirable because novices sometimes accidentally leave their
1009: directory or files world-writable.
1010: The default is
1011: .Dq yes .
1.112 djm 1012: Note that this does not apply to
1013: .Cm ChrootDirectory ,
1014: whose permissions and ownership are checked unconditionally.
1.1 stevesk 1015: .It Cm Subsystem
1.51 jmc 1016: Configures an external subsystem (e.g. file transfer daemon).
1.59 djm 1017: Arguments should be a subsystem name and a command (with optional arguments)
1018: to execute upon subsystem request.
1.80 djm 1019: .Pp
1.1 stevesk 1020: The command
1021: .Xr sftp-server 8
1022: implements the
1023: .Dq sftp
1024: file transfer subsystem.
1.80 djm 1025: .Pp
1026: Alternately the name
1027: .Dq internal-sftp
1028: implements an in-process
1029: .Dq sftp
1030: server.
1031: This may simplify configurations using
1032: .Cm ChrootDirectory
1033: to force a different filesystem root on clients.
1034: .Pp
1.1 stevesk 1035: By default no subsystems are defined.
1036: Note that this option applies to protocol version 2 only.
1037: .It Cm SyslogFacility
1038: Gives the facility code that is used when logging messages from
1.53 jmc 1039: .Xr sshd 8 .
1.1 stevesk 1040: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1041: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1042: The default is AUTH.
1.27 markus 1043: .It Cm TCPKeepAlive
1044: Specifies whether the system should send TCP keepalive messages to the
1045: other side.
1046: If they are sent, death of the connection or crash of one
1047: of the machines will be properly noticed.
1048: However, this means that
1049: connections will die if the route is down temporarily, and some people
1050: find it annoying.
1051: On the other hand, if TCP keepalives are not sent,
1052: sessions may hang indefinitely on the server, leaving
1053: .Dq ghost
1054: users and consuming server resources.
1055: .Pp
1056: The default is
1057: .Dq yes
1058: (to send TCP keepalive messages), and the server will notice
1059: if the network goes down or the client host crashes.
1060: This avoids infinitely hanging sessions.
1061: .Pp
1062: To disable TCP keepalive messages, the value should be set to
1063: .Dq no .
1.118 djm 1064: .It Cm TrustedUserCAKeys
1065: Specifies a file containing public keys of certificate authorities that are
1.120 djm 1066: trusted to sign user certificates for authentication.
1.119 jmc 1067: Keys are listed one per line; empty lines and comments starting with
1.118 djm 1068: .Ql #
1069: are allowed.
1070: If a certificate is presented for authentication and has its signing CA key
1071: listed in this file, then it may be used for authentication for any user
1072: listed in the certificate's principals list.
1073: Note that certificates that lack a list of principals will not be permitted
1074: for authentication using
1075: .Cm TrustedUserCAKeys .
1.119 jmc 1076: For more details on certificates, see the
1.118 djm 1077: .Sx CERTIFICATES
1078: section in
1079: .Xr ssh-keygen 1 .
1.18 markus 1080: .It Cm UseDNS
1081: Specifies whether
1.52 jmc 1082: .Xr sshd 8
1.40 jmc 1083: should look up the remote host name and check that
1.18 markus 1084: the resolved host name for the remote IP address maps back to the
1085: very same IP address.
1086: The default is
1087: .Dq yes .
1.1 stevesk 1088: .It Cm UseLogin
1089: Specifies whether
1090: .Xr login 1
1091: is used for interactive login sessions.
1092: The default is
1093: .Dq no .
1094: Note that
1095: .Xr login 1
1096: is never used for remote command execution.
1097: Note also, that if this is enabled,
1098: .Cm X11Forwarding
1099: will be disabled because
1100: .Xr login 1
1101: does not know how to handle
1102: .Xr xauth 1
1.15 jmc 1103: cookies.
1104: If
1.1 stevesk 1105: .Cm UsePrivilegeSeparation
1106: is specified, it will be disabled after authentication.
1107: .It Cm UsePrivilegeSeparation
1108: Specifies whether
1.52 jmc 1109: .Xr sshd 8
1.2 stevesk 1110: separates privileges by creating an unprivileged child process
1.15 jmc 1111: to deal with incoming network traffic.
1112: After successful authentication, another process will be created that has
1113: the privilege of the authenticated user.
1114: The goal of privilege separation is to prevent privilege
1.1 stevesk 1115: escalation by containing any corruption within the unprivileged processes.
1116: The default is
1117: .Dq yes .
1.134 djm 1118: If
1119: .Cm UsePrivilegeSeparation
1120: is set to
1121: .Dq sandbox
1122: then the pre-authentication unprivileged process is subject to additional
1123: restrictions.
1.137 djm 1124: .It Cm VersionAddendum
1125: Optionally specifies additional text to append to the SSH protocol banner
1126: sent by the server upon connection.
1127: The default is
1128: .Dq none .
1.1 stevesk 1129: .It Cm X11DisplayOffset
1130: Specifies the first display number available for
1.52 jmc 1131: .Xr sshd 8 Ns 's
1.1 stevesk 1132: X11 forwarding.
1.52 jmc 1133: This prevents sshd from interfering with real X11 servers.
1.1 stevesk 1134: The default is 10.
1135: .It Cm X11Forwarding
1136: Specifies whether X11 forwarding is permitted.
1.13 stevesk 1137: The argument must be
1138: .Dq yes
1139: or
1140: .Dq no .
1.1 stevesk 1141: The default is
1142: .Dq no .
1.13 stevesk 1143: .Pp
1144: When X11 forwarding is enabled, there may be additional exposure to
1145: the server and to client displays if the
1.52 jmc 1146: .Xr sshd 8
1.13 stevesk 1147: proxy display is configured to listen on the wildcard address (see
1148: .Cm X11UseLocalhost
1.52 jmc 1149: below), though this is not the default.
1.13 stevesk 1150: Additionally, the authentication spoofing and authentication data
1151: verification and substitution occur on the client side.
1152: The security risk of using X11 forwarding is that the client's X11
1.52 jmc 1153: display server may be exposed to attack when the SSH client requests
1.13 stevesk 1154: forwarding (see the warnings for
1155: .Cm ForwardX11
1156: in
1.19 jmc 1157: .Xr ssh_config 5 ) .
1.13 stevesk 1158: A system administrator may have a stance in which they want to
1159: protect clients that may expose themselves to attack by unwittingly
1160: requesting X11 forwarding, which can warrant a
1161: .Dq no
1162: setting.
1163: .Pp
1164: Note that disabling X11 forwarding does not prevent users from
1165: forwarding X11 traffic, as users can always install their own forwarders.
1.1 stevesk 1166: X11 forwarding is automatically disabled if
1167: .Cm UseLogin
1168: is enabled.
1169: .It Cm X11UseLocalhost
1170: Specifies whether
1.52 jmc 1171: .Xr sshd 8
1.1 stevesk 1172: should bind the X11 forwarding server to the loopback address or to
1.15 jmc 1173: the wildcard address.
1174: By default,
1.52 jmc 1175: sshd binds the forwarding server to the loopback address and sets the
1.1 stevesk 1176: hostname part of the
1177: .Ev DISPLAY
1178: environment variable to
1179: .Dq localhost .
1.8 stevesk 1180: This prevents remote hosts from connecting to the proxy display.
1.1 stevesk 1181: However, some older X11 clients may not function with this
1182: configuration.
1183: .Cm X11UseLocalhost
1184: may be set to
1185: .Dq no
1186: to specify that the forwarding server should be bound to the wildcard
1187: address.
1188: The argument must be
1189: .Dq yes
1190: or
1191: .Dq no .
1192: The default is
1193: .Dq yes .
1194: .It Cm XAuthLocation
1.11 stevesk 1195: Specifies the full pathname of the
1.1 stevesk 1196: .Xr xauth 1
1197: program.
1198: The default is
1199: .Pa /usr/X11R6/bin/xauth .
1200: .El
1.55 jmc 1201: .Sh TIME FORMATS
1.53 jmc 1202: .Xr sshd 8
1.1 stevesk 1203: command-line arguments and configuration file options that specify time
1204: may be expressed using a sequence of the form:
1205: .Sm off
1.7 stevesk 1206: .Ar time Op Ar qualifier ,
1.1 stevesk 1207: .Sm on
1208: where
1209: .Ar time
1210: is a positive integer value and
1211: .Ar qualifier
1212: is one of the following:
1213: .Pp
1214: .Bl -tag -width Ds -compact -offset indent
1.64 jmc 1215: .It Aq Cm none
1.1 stevesk 1216: seconds
1217: .It Cm s | Cm S
1218: seconds
1219: .It Cm m | Cm M
1220: minutes
1221: .It Cm h | Cm H
1222: hours
1223: .It Cm d | Cm D
1224: days
1225: .It Cm w | Cm W
1226: weeks
1227: .El
1228: .Pp
1229: Each member of the sequence is added together to calculate
1230: the total time value.
1231: .Pp
1232: Time format examples:
1233: .Pp
1234: .Bl -tag -width Ds -compact -offset indent
1235: .It 600
1236: 600 seconds (10 minutes)
1237: .It 10m
1238: 10 minutes
1239: .It 1h30m
1240: 1 hour 30 minutes (90 minutes)
1241: .El
1242: .Sh FILES
1243: .Bl -tag -width Ds
1244: .It Pa /etc/ssh/sshd_config
1245: Contains configuration data for
1.53 jmc 1246: .Xr sshd 8 .
1.1 stevesk 1247: This file should be writable by root only, but it is recommended
1248: (though not necessary) that it be world-readable.
1249: .El
1.19 jmc 1250: .Sh SEE ALSO
1251: .Xr sshd 8
1.1 stevesk 1252: .Sh AUTHORS
1253: OpenSSH is a derivative of the original and free
1254: ssh 1.2.12 release by Tatu Ylonen.
1255: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1256: Theo de Raadt and Dug Song
1257: removed many bugs, re-added newer features and
1258: created OpenSSH.
1259: Markus Friedl contributed the support for SSH
1260: protocol versions 1.5 and 2.0.
1261: Niels Provos and Markus Friedl contributed support
1262: for privilege separation.
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